The rapid development of nanoscience and nanotechnology is driving an interest in ultra-thin polymer layers with highly controlled and selective gas barrier properties. New packaging strategies that utilize the unique gas transport characteristics of nanolayers could significantly address growing environmental and energy concerns. Considering the magnitude of the need, packaging with enhanced gas barrier and selectively could dramatically reduce the amount of food waste, thereby reducing world hunger, greenhouse gas generation and the load on global water and energy supplies (A. L. Brody, Food Technology 62(6), 121 (2008)).
Crystallization is a common approach for reducing gas permeability of polymers in the bulk (D. H. Weinkauf, D. R. Paul, in Barrier Polymers and Structures, W. J. Koros. Ed. American Chemical Society, Washington, D.C. 1990), pp. 60-91). Crystallization is a self-organization process through which molecules are arranged in a regular order (M. D. Ward, Science 308, 1566-1567 (2005)). It is fundamental to the structural characteristics and the physicochemical properties of many substances, including inorganic materials, small organic molecules, synthetic polymers and biomacromolecules (V. Cherezov, D. M. Rosenbaum, M. A. Hanson, S. G. F. Rasmussen, F. S. Thian. T. S. Kobilka, H. J. Choi, P. Kuhn, W. J. Weis. B. K. Kobilka. R. C. Stevens, Science 318, 1258-1265 (2007); S. G. F. Rasmussen, H. J. Choi, D. M. Rosenbaum. T. S. Kobilka. F. S. Thian, P. C. Edwards, M. Burghammer, V. R. P. Ratnala, R. Sanishvili, R. F. Fischetti, G. F. X. Schertler, W. J. Weis, B. K. Kobilka. Nature 450, 383-U384 (2007)).
The two-dimensional crystallization of polymers is conventionally studied with polymeric thin films or block copolymers that contain at least one crystallizable block. In the former, crystallizable layers with nanometer to submicron thicknesses are prepared by a solution process such as Langmuir-Blodgett, spin-coating techniques. These approaches are limited by the solvent requirement and by the small amount of material that can be fabricated. In the latter, a lamellar phase morphology on the length scale of a few tens of nanometers can be achieved as a consequence of microphase separation of the dissimilar blocks below the order-disorder transition temperature (TODT) (F. S. Bates, G. H. Fredrickson, Annual Review of Physical Chemistry 41, 525-557 (1990)). Shear-alignment is often necessary to construct well-defined layering with a uniformly oriented, micron-scale phase morphology (Z.-R. Chen, J. A. Kornfield, S. D. Smith, J. T. Grothaus, M. M. Satkowski Science 277, 1248-1253 (1997)).